1. Field of the Invention
The present invention relates to a disk array device and a method of supplying power to a disk array device.
2. Background Art
An apparatus is known in which its storage capacity can be increased by adding devices mounted with disk drives (hereinafter referred to as HDDs). An example of such an apparatus may be a so-called rackmount-type disk array device (or storage device). To the apparatus' rackmount or each of the apparatus' housings are mounted HDD housings. Such an HDD housing may comprise one basic housing as well as other additional housings added as needed. As shown in FIG. 14, each housing contains a plurality of HDDs, an array controller for providing HDD control (hereinafter referred to simply as a “controller”), and various peripheral circuits such as an AC/DC power supply. Such a storage device is disclosed in Japanese Publication No. JP-7-508112-T of International Application No. PCT/US93/04444.
The AC/DC power supply receives AC power (AC input) from the outside, converts it into a direct current (DC), and supplies power to all HDDs and peripheral circuits in the housing. An AC/DC conversion circuit may be mounted on a power supply circuit board in a power supply housing as the AC/DC power supply.
Each AC power inputs (AC input 1 and AC input 2) has its own AC/DC power supply, establishing a duplex AC/DC power supply system. The DC output of each AC/DC power supply is supplied via a power supply line on a motherboard to all HDDs and peripheral circuits, such as an interface control circuit for controlling the interface with the controller.
A backup battery section is also furnished as an uninterruptible power supply (UPS) to provide for any power supply failure. The battery section may be, for example, a secondary battery that stores electrical power and permits discharge. The DC output of the battery section is coupled, by means of ORing, to the DC outputs of the AC/DC power supplies via power supply lines on the motherboard. While a normal operation is being conducted with no power supply failure encountered, the battery section becomes fully charged by the AC/DC power supplies and remains on standby. If a power supply failure occurs, the battery section is discharged to supply power in place of the AC/DC power supplies.
To provide scalability so as to handle mounted HDDs that tend to increase in number, the above disk array devices make it possible to increase the number of HDDs mounted within a housing. In line with the provision of such scalability, it is also demanded that the power supply system be improved.
Various troubles caused by a power supply failure will now be described. If a power supply line is shorted to ground on the motherboard, all the HDDs and the interface control circuit mounted within a housing become inoperative due to the resulting voltage drop. In other words, the entire contents of the housing are adversely affected by the power supply failure. In addition, the power supply failure also adversely affects an interface control circuit that is mounted within another housing and connected to the interface control circuit that has failed. As the influence of the power supply failure is enlarged in this manner, an enormous amount of time and labor will be required to achieve recovery.
If a power supply failure occurs on the motherboard, all the HDDs mounted on the motherboard are rendered inaccessible. As a result, the data stored according to RAID (Redundant Array of Inexpensive Disks) is partly lost. After the motherboard is recovered, it is therefore necessary to recover the lost data from the remaining data and write it back to a HDD that has been recovered. The time required for such a write operation increases with an increase in the HDD storage capacity. If another failure occurs in another HDD or the motherboard before the lengthy recovery procedure is completed, data recovery will no longer be achievable. To minimize the possibility of the occurrence of this situation, it is necessary to use high-reliability, expensive parts with a view toward decreasing the failure rate of HDDs, motherboard, and other relevant components.
Even if a power supply failure occurs in a HDD, controller, or other component on the motherboard, it affects the motherboard and lowers the supply voltage. As a result, all the HDDs mounted on the motherboard become inoperative.
A problem caused by an increase in the number of HDDs on a motherboard will now be described. When the mounted HDDs increase in number, their load current increases. Voltage noise then increases due to the fluctuation of the increased load current. As a result, voltage stability cannot be maintained.
Further, the increase in number of HDDs may cause a voltage drop due to power supply failure or noise increase within a conductive pattern on the motherboard, which supplies power to the HDDs. To avoid such a trouble, it is necessary to ensure that the conductive pattern thickness and width are adequate. However, this requires the motherboard to be increased in the number of conductive pattern layers. As a result, the motherboard thickness increases, thereby raising the motherboard price.
A problem caused by HDD hot-plugging/hot-unplugging will now be described. If a HDD is hot-plugged to a live power supply line on the motherboard, an inrush current to the HDD arises. The power supply line voltage becomes unstable due to the inrush current so that the stability of the voltage supply to the activated HDD cannot be maintained. To avoid this trouble, it is necessary to add a new circuit for inhibiting the inrush current that may arise upon HDD hot-plugging.
The balance between two AC inputs for a duplex AC power supply will now be described. If the power consumption varies in accordance with the operation states of the installed HDDs, unbalance results because the two AC inputs cannot be equally divided.
A power supply failure that may occur during destaging will now be described. If the AC input to disk array devices is lost due, for instance, to a power failure, the battery section will supply power so that the data stored in the controller's cache can be written into each HDD. However, the battery section must supply power to all HDDs and cannot limit the power supply destination to a HDD that is about to store data. More specifically, power supply control cannot be exercised on an individual HDD basis so that, until destaging is finished, the battery section is forced to supply power to all HDDs including the ones that do not have to operate. As a result, the capacity of the battery section needs to be increased. Such a capacity increase causes an increase in size, weight, and price.
Meanwhile, an FET, relay, or other switching device can be mounted in the power supply path to each HDD to enable the battery section to selectively supply power to a specific HDD. Such a switching device can be turned OFF to shut off the power supply to a HDD that does not have to operate. The use of this method makes it possible to minimize the power consumption and avoid increase in the capacity of the battery section. However, while a normal operation is conducted with no failure encountered, that is, while the HDDs receive power supply from an AC power supply and operate normally, a voltage drop or noise generation may occur due to the on-resistance of an FET or other switching devices in the power supply path. Therefore, a switching device should not be mounted in the power supply path leading to each HDD.
No matter what the HDD storage capacity is, it is also necessary to furnish an AC power supply and battery section that are capable of supplying power adequate for the maximum number of HDDs that can be mounted within a housing. Therefore, if an unexpectedly small number of HDDs are mounted, not only does the power efficiency deteriorate, but also the size and price of a disk array device increase due to the use of an unnecessarily large AC power supply and battery section.